External Air Compressor Connection

Topic: External Air Compressor Connection (Read 1422 times) previous topic - next topic

External Air Compressor Connection

October 26, 2014, 08:00:34 pm

I've been reading up on connecting a compressor to the aux air connection (on my coach it is in the LP bay) to pressurize the system so that the coach can be leveled and the brakes released.

After a week or more my air pressure guages for the front and rear tanks read close to zero. If I connect my compressor to the aux air connection the compressor will run if the ignition is on but I don't see any increase in the tank air pressure and I cannot release the emergency brake.

What is supposed to happen? Is something not working correctly? What is the 12v compressor pumping up? I am not sure I have a good schematic of the air system.

Thanks

Roger

Re: External Air Compressor Connection

Reply #1 – October 26, 2014, 08:22:33 pm

Roger I have a secondary air compressor as well and looked the other day to see what it's function was and the best I can tell it was for service. I also have a valve coming off my main system that has a air line connection and was wondering what that would be for. Now on my Bus I used my secondary compressor to do what your talking about and it worked great and I could air up the bus without starting the motor and kill a bunch of mosquito's. I had a switch that I would flip and it would start the compressor when I was hooked up to the pole. I did have a one way valve in the line so it would not feed back into the compressor. Not sure if that helps any.

Re: External Air Compressor Connection

Reply #2 – October 26, 2014, 08:26:09 pm

Quote from: Home2fromHastings – October 26, 2014, 08:00:34 pm

I've been reading up on connecting a compressor to the aux air connection (on my coach it is in the LP bay) to pressurize the system so that the coach can be leveled and the brakes released.

After a week or more my air pressure guages for the front and rear tanks read close to zero. If I connect my compressor to the aux air connection the compressor will run if the ignition is on but I don't see any increase in the tank air pressure and I cannot release the emergency brake.

Are you talking about connecting an external (let's say pancake-style) air compressor to the aux connection, or are you talking about flipping a switch next to the driver's seat that's marked something like "air tank" which causes the on-board HWH aux compressor to run?

Re: External Air Compressor Connection

Reply #3 – October 26, 2014, 08:30:11 pm

Hi Roger,
On my 1997 U320 I connect my portable (external) compressor to the air line in the propane compartment. The outlet just above the propane tank, and next to the drawer. I set my portable compressor to one hundred pounds on the regulator. I plug it in and it fills my system. I disconnect the compressor. Guages on dash go to almost one hundred pounds. I can raise and lower the coach. I hope this is what you were talking about!
Raymond

Re: External Air Compressor Connection

Reply #4 – October 26, 2014, 08:54:00 pm

I used an "outboard" 120VAC compressor to "air up" the coach one time. I connected it via the accessory air port in the propane bay. When I disconnected the air line, I saw a big puff of moisture escape and dissipate into the atmosphere. I proved the concept of airing up the coach without running the engine, but decided it was a bad idea to introduce moisture into the air system with the outboard compressor that has no effective air dryer.

On our 1997 coach, the 12VDC compressor appears to only supply pressure to the HWH leveling system while in "Level" mode. It will not provide pressure to the brake system. Also, it does not have a highly effective system for extracting moisture from the compressed air.

Re: External Air Compressor Connection

Reply #5 – October 26, 2014, 09:11:54 pm

Michelle and all, yes, I am connecting my 110v pancake compressor to the aux air line connection in the LP bay. I have an inline air dryer so that I am not introducing moisture into the system. I have direct read mechanical pressure guages on the front and rear tank. They do not show an air pressure increase when the external compressor is connected. Emergency brakes do not release (no air).

On the 2001 U320 the switch Michelle asks about does not exist. Not sure what it does if it did. I would like to add one but I don't really know what it does. It would be nice to just turn the power to the 12v compressor off.

Does anyone have a schematic of the air system on the 2001 and on the 2003 (Michelle's coach year, I think) so I can see the difference.

Maybe I have a bad component somewhere.

Roger

Re: External Air Compressor Connection

Reply #6 – October 26, 2014, 09:15:25 pm

Quote from: Home2fromHastings – October 26, 2014, 09:11:54 pm

On the 2001 U320 the switch Michelle asks about does not exist. Not sure what it does if it did.

It opens a solenoid that allows the HWH 12V aux compressor to feed the (I think) wet tank. Primary purpose is to start airing up the coach before departing a campground without running the big Cummins - a courtesy to other campers. Note I said "start airing up". It doesn't come close to replacing actually running the coach engine-driven compressor.

Re: External Air Compressor Connection

Reply #7 – October 26, 2014, 10:06:25 pm

I removed the original fittings from both tanks.
Replaced then with Female pneumatic quick disconnects.
Use clear plastic baggies & Zip tie's for weather and road protecting.
To drain ( have never seen any ) moisture I use a blow gun with a male quick disconnect.
I drain the "wet" tank each time I pass it.

Re: External Air Compressor Connection

Reply #8 – October 26, 2014, 11:19:27 pm

Roger, the aux compressor is not designed to fill your main tanks and there is not switch on your dash to do so if yours is like our 01. There is a good chance you will burn out the aux compressor if you run too long though I had mine run quite long as it tried to do that filling before I pulled the fuse.. Now I have a switch on the aux so I can stop it rather than pulling the fuse.

I am told some models do have a proper aux compressor and the switch by your left window that do allow you to fill the tanks without cranking your engine, and was said to keep from being engine noise if trying to leave early in the morning without disturbing others for a while! Well, what I was told.

The aux comoressir is more intended to keep you level and the bladder operable. It as far as I can tell is meant to stay separate from your rear and front brake tanks by check valves. I too have mechanical gauges.

If those tanks are going to zero, you may have the check valve failing that keeps those pressures from leaking back to the wet tank. I can stay at 70 psi for weeks.

That is what I understand and have experienced Best I can tell....though I may misunderstand what I have been told were the causes. so let's see what others say.

Re: External Air Compressor Connection

Reply #9 – October 27, 2014, 12:44:37 am

The check valves do stop return air from happening but air from tank can also drain out of the treadle valve (for brakes) if the seals or fittings are not holding. Also slide over stairs and step valve are favourite places for leaks.
JohnH

Re: External Air Compressor Connection

Reply #10 – October 27, 2014, 10:25:20 pm

Roger, some of the later coaches have a check valve at the wet tank where that aux connected hooks you might see if yours has one . My 1996 U270 does not ,I use it all the time when I want to add air to coach air system. Works great I don't have to start engine to put air in before trip. I do use a really good air dryer in my air system in my garage , I use air tools all the time when working on cars or whatever.
Regards,Irwin

Re: External Air Compressor Connection

Reply #11 – October 27, 2014, 11:30:42 pm

Barry Beam sent me air schematic for my year (2001) and the 2002-3 coaches. It looks like external compressor should add air to the front and rear brake tanks but it doesn't happen. Barry suggested that as built and the drawing are not always the same. Time to crawl under the coach (with safety stands of course)

Roger

Re: External Air Compressor Connection

Reply #12 – October 28, 2014, 09:10:27 am

I only use the air connection in LP tank compartment to raise the coach without starting engine, yes I have a water separator on the shop 175 psi 21 cfm supply line. Works for me. Otherwise the coach is lowered to stops while in the garage.

Re: External Air Compressor Connection

Reply #13 – October 28, 2014, 10:36:38 am

That's a big compressor, Dave. I am going to hook my puny air compressor (by comparison) up to the air connection (with an air drier in line) and see if the coach goes up and down. Then I have to see if the plumbing is as the drawing says.

When I park in the barn the coach is a ride height. I shut it off, usually disable the HWH air compressor (I added a switch) and the coach will stay level and and near ride height for weeks. If the HWH compressor is on it cycles occasionally for changes in air temp and when I open the door end get in.

So what is the advantage to dropping the coach down to the stops? Good for the air bags?

Roger

Re: External Air Compressor Connection

Reply #14 – October 28, 2014, 12:14:20 pm

Roger,
Lowering makes easy enter/exit and with the level system turned off, no need for the on board 12 VDC compressor to run very much, installed a on/off switch for that too.

Yes the shop compressor is about big enough, the 175 psi makes the air tools jump about right, many air wrenches, 3/8" to 1" and air over hydraulic roll around jacks. Getting old requires better tools.

Re: External Air Compressor Connection

Reply #15 – October 29, 2014, 11:44:39 am

Roger, I was wrong in stating that my coach was holding at "70" psi on the mechanical gauged left and right tanks. with Level off.

I tried an experiment after I heard the aux compressor running yesterday.....I have the switch like Dave M....so turned off the aux compressor. (before that turn off, it ran 5 minutes putting air at least in the two tanks, perhaps some air went too into the smaller front tank?, to get back to 68 psi on the two tanks that I can read the pressure)

In 16 hours, for my trial, those two front tanks dropped in pressure from 68 psi to 62 psi....so, that aux compressor had been keeping some pressure in those.

Now I need advice....do I leave the aux "on" so I have pressure to keep the bladder filled? I do not have "level on"

Ideas?

Re: External Air Compressor Connection

Reply #16 – October 29, 2014, 02:44:46 pm

Mike,
My slide bladder seal stays snug for weeks with the compressor off, the big reason I added the disconnect switch to the compressor, as not needed unless want to move the slide, then pump up.

Re: External Air Compressor Connection

Reply #17 – October 29, 2014, 07:15:09 pm

From the plumbing diagram it looks like the HWH compressor feeds the wet tank which then feeds the front and rear brake tanks.
But there must be an ignition switched solonoid valve that isolates the wet tank if the ignition is off.
The brake tanks (which is what your guages read) bleed off over time with the ignition off but the HWH compressor still keeps the slide bladder full and the coach level.
With the HWH compreesor switched off my coach stays level and the bladder full for a long time (weeks or more).

Still not sure what is going on here

Roger

Re: External Air Compressor Connection

Reply #18 – October 29, 2014, 07:27:18 pm

Roger, I hate to reply again with only minimal info....hope this small part helps. I went out to see Mr. Risch. He said something going on, bring it in. Should not be leaking down as it is, should not be using the aux to pressurize the left/right front tanks. As I said above, level off, aux switched off, leaked from 68 psi to 62/63 psi in about 16 hours

I cannot say if he means it should not work that way, that the aux will do that, or it should not have to do so.

However both check valves were replaced only a couple of weeks ago

I long ago learned to follow Dave's lead and think that would be the right way to operate. But I hate if something not doing as it should. Not a good trait I think, but...

Mike

Re: External Air Compressor Connection

Reply #19 – October 29, 2014, 07:33:47 pm

Quote from: Home2fromHastings – October 29, 2014, 07:15:09 pm

From the plumbing diagram it looks like the HWH compressor feeds the wet tank which then feeds the front and rear brake tanks.
But there must be an ignition switched solonoid valve that isolates the wet tank if the ignition is off.
The brake tanks (which is what your guages read) bleed off over time with the ignition off but the HWH compressor still keeps the slide bladder full and the coach level.
With the HWH compreesor switched off my coach stays level and the bladder full for a long time (weeks or more).
Still not sure what is going on here
Roger

There is a check valve on the back of the Front & Rear Tanks isolating them grom the wet tank when engine is off.
There is a check valve on the Front of the Front & Rear Tanks isolating the brakes from the leveling system & slide.
So if Dash gauges go down (Brakes) the leveling system could still work fine if no leaks.
Slide bladder only needs 12 psi.

Re: External Air Compressor Connection

Reply #20 – October 29, 2014, 08:05:18 pm

Barry, it looks like the wet tank line into the front and rear tanks has one way check valves at the tanks preventing air from returning to the wet tank. Maybe I am reading the drawing wrong. Maybe the symbols indicate a solenoid valve?

I need to get underneath while I can. It only got to 41° today.

Thanks for everyone's input.

I am concerned about releasing the parking brake if there is no air and no engine. I understand there is a mechanical release.

Roger

Re: External Air Compressor Connection

Reply #21 – October 29, 2014, 11:06:42 pm

Quote from: Home2fromHastings – October 29, 2014, 08:05:18 pm

Barry, it looks like the wet tank line into the front and rear tanks has one way check valves at the tanks preventing air from returning to the wet tank. Maybe I am reading the drawing wrong. Maybe the symbols indicate a solenoid valve?
Roger

They are check valve as stated below.
"There is a check valve on the back of the Front & Rear Tanks isolating them grom the wet tank when engine is off."
It is not a solenoid.

Re: External Air Compressor Connection

Reply #22 – October 30, 2014, 02:21:36 pm

and they only cost $10 to replace too. The only suggestion I have if anyone is changing them out is-Do NOT take them apart to install into tank as the wall thickness is very thin and the valve body WILL distort with wrench and be useless to assemble the mating part.
other than that a simple process.
JohnH

Re: External Air Compressor Connection

Reply #23 – October 30, 2014, 08:28:41 pm

Home2fromHastings,
You should come to Texas, I'm at the deer lease in Falfurrias today, and it's 86 degrees! Nice. Gotta love winter in Texas.

Re: External Air Compressor Connection

Reply #24 – October 30, 2014, 09:10:19 pm

27° tonight. Texas in January. It is just starting to get to the point where the shorts get put away.

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